Control valves are employed in a variety of fluid systems and applications to control the operation of hydraulic and pneumatic machinery, for example. In general, a directional control valve is configured to enable definition of a variety of different internal pathways through which a fluid can flow. Changes to these different pathways can be effected with the use of a spool that moves within a chamber. The body of the spool can be configured to interface with the chamber structure such that as the spool moves within the chamber, the spool may close off one or more fluid pathways, while opening up one or more other fluid pathways. In this way, the spool controls the flow of a fluid through the control valve. Movement of the spool can be achieved with the use of a pressurized control fluid that acts on different portions of the spool to move the spool to/from a desired position.
Because a control valve relies for its operational effectiveness on the positioning of the spool in one or more specific operational positions, it is important to the operation of the control valve to ensure that the spool does not remain in a position other than one of the specific operational positions. Accordingly, some control valve designs include one or more springs, each of which serves to bias the spool toward a particular one of the specific operational positions. In this way, the springs are able to prevent the spool from remaining in some intermediate position that is other than one of the specific operational positions, and the springs thus contribute to the operational effectiveness of the control valve.
While springs such as those described above provide some benefits, they can nonetheless be problematic. For example, because springs are mechanical components, they wear out over time. In particular, the physical contact between the springs and the spool/chamber can contribute to wearing of the springs, and the spool/chamber in some cases. As the springs wear, they may shed metal and/or other particles. Likewise, components in contact with the springs may shed metal and/or other particles as well. This wearing of the springs may manifest itself, for example, as reduced control valve performance. Eventually the control valve performance deteriorate to the point that the springs require replacement. Typically, replacement of the springs involves disassembly and reassembly of the control valve, which can be expensive and time consuming.
In light of these, and other, problems, it would be useful to be able to be able to provide a control valve configured so that the spool does not remain in a position other than one of the specific operational positions. It would also be useful to be able to move the spool to specific operational positions in a manner that reduces, or eliminates, the mechanical wearing associated with designs that employ springs for this purpose. As well, it would be useful to be able to bias the spool into each of a plurality of different operational positions.